M.S. de Queiroz

A continuous asymptotic tracking control strategy for uncertain nonlinear systems

In this note, we present a new continuous control mechanism that compensates for uncertainty in a class of high-order, multiple-input-multiple-output nonlinear systems. The control strategy is based on limited assumptions on the structure of the system nonlinearities. A new Lyapunov-based stability argument is employed to prove semiglobal asymptotic tracking.

Nonlinear control of active magnetic bearings: a backstepping approach

In this paper, the authors utilize a nonlinear model of a planar rotor disk, active magnetic bearing system to develop a nonlinear controller for a full-order electromechanical system. The controller requires measurement of the rotor position, rotor velocity, and stator current and achieves global exponential rotor position tracking. Simulations are provided to illustrate the performance of the controller.

A discontinuous output feedback controller and velocity observer for nonlinear mechanical systems

In this paper, we develop a new discontinuous output feedback tracking controller for a class of uncertain, nonlinear, multi-input/multi-output, mechanical systems whose dynamics are first-order differentiable. A novel filter design and Lyapunov-type stability analysis are used to prove semi-global asymptotic tracking. As a by-product of the proposed framework, we also present the design of a new simple, discontinuous velocity observer that ensures global asymptotic velocity observation.

Brief Adaptive tracking control using synthesized velocity from attitude measurements

The attitude tracking control problem of uncertain rigid spacecraft without angular velocity measurements is addressed in this paper. The adaptive control law, which incorporates a velocity-generating filter from attitude measurements, is shown to ensure the asymptotic convergence of the attitude and angular velocity tracking errors despite unknown spacecraft inertia. Simulation results are presented to illustrate the theoretical results.

Robust adaptive asymptotic tracking of nonlinear systems with additive disturbance

This note deals with the tracking control of multiple-input-multiple-output (MIMO) nonlinear parametric strict-feedback systems in the presence of additive disturbances and parametric uncertainties. For such systems, C/sup 0/ robust adaptive controllers usually cannot ensure asymptotic tracking or even regulation. In this work, under the assumption the disturbances are C/sup 2/ with bounded time derivatives, we present a C/sup 0/ robust adaptive control construction that guarantees the tracking error is asymptotically driven to zero.

Tracking Control of Robot Manipulators with Bounded Torque Inputs

This paper examines the problem of link position tracking control of robot manipulators with bounded torque inputs. An adaptive, full-state feedback controller and an exact model knowledge, output feedback controller are designed to produce semi-global asymptotic link position tracking errors. Simulation results are provided to validate the theoretical concepts, and a comparative analysis demonstrates the benefits of the proposed controllers.

Robust Visual-Servo Control of Robot Manipulators in the Presence of Uncertainty

This paper considers the problem of position control of planar robot manipulators via visual servoing in the presence of uncertainty associated with the robot mechanical dynamics and the camera system for both fixed-camera and camera-in-hand configurations. Specifically, we first design a robust controller that compensates for uncertainty throughout the whole robot-camera system and ensures global uniformly ultimately bounded position tracking for the fixed-camera configuration. Under the same class of uncertainty, we then develop a setpoint controller for the camera-in-hand configuration that achieves global uniformly ultimately bounded regulation. Experimental results illustrating the performance of both controllers are also included.

Robust visual-servo control of robot manipulators in the presence of uncertainty

This paper considers the problem of position control of planar robot manipulators via visual servoing in the presence of uncertainty associated with the robot mechanical dynamics and the camera system for both fixed-camera and camera-in-hand configurations. Specifically, we first design a robust controller that compensates for uncertainty throughout the whole robot-camera system and ensures global uniformly ultimately bounded position tracking for the fixed-camera configuration. Under the same class of uncertainty, we then develop a setpoint controller for the camera-in-hand configuration that achieves global uniformly ultimately bounded regulation.

A sufficiently smooth projection operator

In this note, we introduce a new parameter projection operator for adaptation laws. The projection operator replaces the common Lipschitz continuity property with the stronger property of arbitrarily many times continuous differentiability. The proposed projection is useful for backstepping-based, robust adaptive controllers which require multiple differentiations of the adaptation law.

Task-space tracking control of robot manipulators via quaternion feedback

In this paper, we consider the problem of task-space tracking control of robot manipulators. Based on a quaternion representation of the end-effector orientation, we design a class of task-space controllers that ensure asymptotic end-effector position and orientation tracking. To facilitate the control design, we first develop model-based and adaptive full-state feedback controllers. We then present a model-based output feedback controller that eliminates link velocity measurements via a model-based observer. The application of the proposed control strategy to redundant robots is also discussed. Simulation results based on a six-link manipulator system are presented for the output feedback controller.